1. Field of the Invention
The invention relates to a shift control apparatus and shift control method for an automatic transmission, which executes a torque reduction control when downshifting in response to a downshift determination made during an upshift.
2. Description of Related Art
In Japanese Patent Publication Laid-Open No. 2001-124193 a shift control of an automatic transmission for changing the speed of a rotation transferred from a power source to an input member, and outputs the rotation to a drive wheel, is described. During an upshift, in which a first friction coupling device is engaged, the operation of the accelerator by the driver may cause a downshift command to be output. When the transmission downshifts, the first friction-coupling device is disengaged and a second friction-coupling device is engaged. Accordingly, the engine may overspeed, and the downshift cannot be performed appropriately. The described shift control addresses this problem by delaying the downshift, in spite of the downshift command, for a predetermined time. In addition, Japanese Patent Publication Laid-Open No. 8-244499 describes the technology for starting the downshift in response to the downshift determination, and executing a torque reduction control for reducing the torque of the power source during the downshift so as to prevent overspeeding of the engine and to decrease the shift shock.
In Japanese Patent Publication Laid-Open No. 2001-124193, because the downshift is delayed, there is a lag between the operation of the accelerator pedal and output of the desired driving force through the downshift operation. Meanwhile, in Japanese Patent Publication Laid-Open No. 8-244499, the downshift operation starts immediately in response to the downshift command and the torque reduction control is executed simultaneously. The downshift operation is then performed under the condition where the torque of the power source is suppressed. Accordingly, much time is taken for the rotational speed of the input member to increase to the synchronous rotational speed of a gear stage after the downshift operation. Again resulting in a time lag between operation of the accelerator pedal and output of the desired driving force.